Today Father Jerzy Popiełuszko, the "priest of Solidarność" – the freedom movement that saw the eventual fall of communism in Poland – will be beatified in Warsaw. Killed by communist agents in the early 80s, Popiełuszko became the symbol of the Polish struggle for liberty in the face of the political oppression of the postwar years, and is now being recognised as a Catholic martyr. His example shows us that saints who were political dissenters, inspired as much by love of their country and of justice as by love of God, can transcend boundaries between religious and secular.

Priest of St Stanisław Kostka church in Warsaw, Popiełuszko was involved in Solidarność from its inception, saying mass at the Gdańsk shipyard strike of August 1980, the founding event of the movement. As the communist authorities cracked down on Solidarność members, Popiełuszko became outspoken in his opposition to the regime, preaching to as many as 50,000 people at his weekly sermons calling for justice and liberty for Poland.

A thorn in the side of the authorities, in October 1984 Popiełuszko was kidnapped and beaten to death by secret police agents. He was 37. Some 800,000 people attended his funeral and his grave at St Stanisław's became a rallying point for Solidarność, as well as a place of Catholic pilgrimage. Today, a museum in the basement of the church places as much emphasis on Popiełuszko's political significance as his spiritual achievements, containing a room festooned with Solidarność banners and a memorial to the movement's martyrs.

Unsurprisingly, it was John Paul II – a Polish pope, famous for his saint-making – who set the process of Popiełuszko's beatification in train in 1997. Popiełuszko was a reminder of the Pope's explicit support for Solidarność in the 80s and his role in the fall of communism in his native Poland, and he described Popiełuszko as "the patron of [Poland's] presence in Europe".

Indeed, at today's beatification, this charismatic priest will be honoured as a national hero as much as a religious one, with representatives of the Polish government prominent among the attendees. Seventy three Polish towns have streets dedicated to Popiełuszko and last year a film of his life, Popiełuszko. Wolność jest w nas (Popiełuszko. Freedom is inside us), brought his story to a general audience – he has become a part of Polish popular culture, and this is entirely independent from his religious associations.

On his future canonisation, Popiełuszko will take a place alongside another Polish saint – Maximilian Kolbe. A Franciscan friar at a monastery near Warsaw, during the Nazi occupation Kolbe turned the presses he had installed for printing Christian magazines over to the production of patriotic literature. He also broadcast resistance messages over the radio, aided the Polish underground and sheltered Jewish refugees, his community caring for some 1,500 people at a time when the Holy See was silent about the Nazi persecution of the Jews of Europe.

Arrested by the Gestapo for his resistance activities in May 1941, Kolbe was sent to Auschwitz, where he later volunteered to take the place of a man chosen for execution in collective punishment for the escape of another prisoner. Left to starve along with nine others, Kolbe was the last survivor of the group when he was killed by lethal injection. His compassion for other prisoners and preservation of his faith in the camp inspired the young Popiełuszko, who was already heavily involved with the struggle for freedom in Poland by the time of Kolbe's canonisation in 1982.

These are saints whose reach goes far beyond the narrow limits of Catholic devotion. Depicted in church art wearing the striped uniform of the victims of the concentration camps, Kolbe represents the defining tragedy of the 20th century, under which Poland suffered most of all. In the many photographs of him, Popiełuszko exudes quiet dignity, symbolising the strength of the Polish people in the postwar decades.

Neither Kolbe nor Popiełuszko were martyred for their faith, as the church claims, but rather were killed for their political dissidence, and as such they offer a focus for remembrance of all who have courageously defied authoritarian regimes. These are not the rarefied "insider" saints of the Catholic church – popes, ascetics and theologians – but people of action and conviction, acting on the basis of universal principles of freedom and human rights. Whether we believe in their miracle-working and church-defined sanctity or not, their commitment to those principles and the magnitude of their bravery exercises a power over us all.